This invention relates to the preparation of urethanes and, more particularly, to the preparation of aromatic urethanes by reaction between aromatic amines, alcohols, and carbon monoxide.
Aromatic urethanes have many important industrial and medical uses, including the preparation of drugs, such as tranquilizers and muscle relaxants, the production of herbicides and insecticides, and the preparation of isocyanates, important building blocks for the production of polyurethanes.
Increasing interest in aromatic urethanes has led to investigations for more economical and efficient processes for their production. Recent research has been directed to the preparation of urethanes by the carbonylation reaction between amines, alcohols, and carbon monoxide using various metal catalysts. Unfortunately, these reactions have been generally catalyzed by expensive Group VIII noble metal catalysts, such as the salts of palladium and platinum. Some success has been observed in the oxidative carbonylation of aliphatic and heterocyclic amines to urethanes with carbon monoxide and alcohols using relatively inexpensive copper salts.
Netherlands Patent No. 94,613 discloses the preparation of urethanes by reacting amines, alcohols and carbon monoxide using copper compound catalysts. Although this patent recommends that the reaction be carried out in the absence of water, there is no teaching of the use of water removal means. Other publications suggest that the presence of water favors carbamate production in this reaction. For example, West German Patent No. 1,105,866 which discloses the preparation of urea compounds by the carbonylation of amines with carbon monoxide using copper compounds, states that drying agents can be added to the reaction mixture to substantially eliminate the production of carbamates.
Since carbon monoxide is a very inexpensive starting material and copper salts are relatively inexpensive catalysts, the preparation of aromatic urethanes from amines, alcohols and carbon monoxide using copper salt catalysts is potentially of considerable economic importance. Accordingly, it would be desirable to adapt this procedure to the preparation of aromatic urethanes from aromatic amines.